1. Field of the Invention
This invention relates to a method for cleaning wells for the production of oil or gas, collectively referred to as oil wells.
2. Description of the Related Art
During completion or workover of an oil well, it is necessary to clean out the well bore before it can be used to carry oil or gas up to the well head. For example, after drilling, perforating, or cementing operations, a large amount of particulate matter removed from the sides of the well bore during such operations remains in the well bore, and it is desirable to remove such particulate matter from inside the well bore prior to production.
A typical method of removing particulate matter from a well bore is to circulate a liquid, referred to as a completion fluid, through the well bore to carry the particulate matter to the surface. A completion fluid commonly comprises an aqueous saline solution, such as sea water or a man-made brine, and the term here is used to include both displacement fluids and completion brines. The drag force acting on particulate matter suspended in a well bore increases with the square of the particle size, and an increased drag force increases the sweeping efficiency of the completion fluid, i.e., the ability of the completion fluid to remove particles from the well. Therefore, the larger the size of the particulate matter, the more efficiently can well cleaning be performed.
It has been found that even under turbulent flow conditions such as generally exist during oil well cleaning, a polymeric flocculant has the ability to agglomerate contaminants into large, low density flocs, which can be readily carried to the surface by the completion fluid. The larger and lighter the flocs, the more efficiently they can be flushed from the well bore. Thus, it is desirable to make the flocs as large and as light as possible.